syms x
D1 = simple(cos(x)^4+tan(x)^4)
D2 = simple(2*cos(x)^2-tan(x)^2)
D3 = simple(cos(x)^2-tan(x)^2)
D4 = simple(cos(x)+(-tan(x)^2)^(1/2))
D5 = simple(cos(x)+i*tan(x))
D6 = simple( (x+1)*x*(x-1))
R7 = simple(x^3+3*x^2+3*x+1)
[D8,how] = simple(cos(3*acos(x)))
